There have been developed base-isolation devices that cause a structure to rise so as to prevent earthquake vibrations from being transmitted to the structure so as to protect the structure from the earthquake. Patent Document 1, for example, discloses a base-isolation device that is configured such that an upper base on which a building is placed is provided so as to contact the surface of a lower base, which is on the ground, and to introduce pressurized gas between the lower surface of the upper base and the upper surface of the lower base, thereby causing the upper base to rise from the lower base, thereby lifting the building. However, although this base-isolation device of Patent Document 1 can lift an ordinary house, it would be extremely difficult for that device to lift a heavy structure such as a high-rise building or a nuclear-power reactor.
Patent Document 2 discloses a base-isolation device that is intended to be used for heavy nuclear-reactor structures. In this device, multiple partitioned spaces are formed underneath a nuclear-reactor structure, between the bottom of the structure and its foundation in the ground, and the partitioned spaces are filled with a pressurized fluid such as oil or water, so as to isolate the nuclear-reactor structure from vibrations of the ground during an earthquake. However, even in an ordinary state in which no earthquake is occurring, pressurized fluid must continue to be filled into this device, which is rather troublesome. In addition, this device does not cause the nuclear-reactor building to rise, and therefore if vibrations due to an earthquake are large, the vibrations might be transmitted to the building and cause damage.